5 Caveats About The Autism And Air Pollution Study

English: A schematic of the global air pollution. The map was made by User:KVDP using the GIMP. It was based on the global air pollution map by the ESA (see http://www.esa.int/esaEO/SEM340NKPZD_index_0.html , http://esamultimedia.esa.int/images/EarthObservation/pollution_global_hires.jpg ) (Photo credit: Wikipedia)

Did you read about it? Air pollution levels within a certain range during a woman’s pregnancy and her baby’s early months are linked to an increased risk for autism! The news stories covering this latest “X linked to Autism study” often include commentary only from the report’s lead author, Heather Volk, Ph.D., M.P.H., at the University of Southern California, but no outside comment or critique on the findings. One example is the Time Healthland article headlined “Autism and Air Pollution: The Link Grows Stronger,” which calls the report part of a “mounting body of evidence,” even though the only other findings suggesting a traffic pollution association is a previous, much-critiquedpaper from the same author group.

The Houston Chronicle parrots study findings with no outside comment, ditto the LA Times. US News, tritto, and Reuters Health, quattro (cuatro?). CBS News says “Autism risk increases with air pollution exposure,” but does include a brief outside comment that doesn’t directly address the study. Indeed, the only two commenters on most of the articles I find are Volk and Geraldine Dawson, chief science officer at Autism Speaks. Dawson is author of an editorial discussing a trio of papers, including the autism-air pollution report, in the latest issue of JAMA Psychiatry (formerly Archives of General Psychiatry). More on that later. But have we just given up on getting outside comment or critique? Thanksgiving is probably to blame.

I’ll step up here now with a little outside comment. Here’s a list of five reasons you should take the “Air pollution linked to autism” headlines with a salt shaker in hand.

1. As some of the above-linked articles eventually get around to noting, this report shows a mathematical association between traffic air pollution components in a certain range, as the authors calculated them, and an increased autism risk. It does not show that air pollution causes autism.

2. The editorial accompanying this research article and many of the newspaper stories describing it highlight the increasing prevalence of autism, implying that perhaps air pollution is to blame. The problem? Air pollution is actually decreasing and hit a 10-year low in 2012. And values have been steadily decreasing since 1970. These graphs reflect changes in air pollution levels over the years for the components that this study tested. You can see an overall decline, sometimes steep, something that doesn’t fit with the increased autism prevalence over the same period, whether you consider the mounting numbers an “epidemic” or a more accurate reflection of primarily stable values over time. Turn to some of the world’s most air-polluted cities, and you will fail to find autism rates that correlate.

3. The study tried to evaluate air pollution exposure where the women lived while pregnant and where their children lived in their first year, comparing children with autism and children without. They report that children with autism were more likely to have lived in an area with higher pollution values. But the analysis doesn’t seem to have taken into account if the women worked or where, how much time they spent outdoors rather than in, or whether or not the children attended a daycare away from their residence. Spending most of your waking hours elsewhere surely would confound data collection focused only on where your residential address is located. If a woman lived in a low-pollution area but commuted to and worked in a smoggy downtown … well, that would make a difference.

4. The numbers for air pollution are several steps removed from direct measurements. The authors captured the autism data through facilities providing services and performed parent interviews. They did their best also to track residential addresses for the women during their pregnancies and for the children after birth. But the air pollution data? Here’s what it went through: A model to estimate average concentrations at specific locations and time periods. Then tossed into the pot were “roadway geometry data,” except that these were from 2005 and the authors wanted 1997-2008, so they “scaled” them, using an estimate of growth, than in turn was based on another kind of data about county vehicle-miles traveled. They then included traffic counts for specific roadways (as a way of looking at traffic pollution), except that values for some roadways weren’t available, in which case they estimated the data based on median volumes for similar sorts of roads in similar regions. They then added in meteorological data from 56 local weather stations, matched to the dates and locations of interest, and used another model to derive values for average emissions. They report nitrogen oxide concentrations, except not really–instead the values are for a “mixture” of air pollution components that serves as a proxy for these concentrations. For values for particulate matter in the air, ozone, and nitrogen dioxide, they based their information on monthly air quality data that they “interpolated” to ambient concentrations using “weighting.” They also used what they call “pseudostations” and “theoretical locations” to fill in various gaps. So, what we have here is model on model on estimate on extrapolation on proxy on interpolation on weighting, which leaves us–I’ve lost track–how many degrees of separation away from direct measurement of air pollution? I’m not saying that kind of measurement is feasible for a large study. But I am saying that the above should temper somewhat any assertions about links between air pollution and autism.

5. The paper appears to be paywalled, but you can view its two graphs at this link. On the vertical axis of each graph is the probability of autism. On the horizontal axis of each graph, we have total traffic-related air pollution exposure, increasing in parts per billion (a part here would be a drop in a billion drops) from left to right. The solid line in the graph is the line of interest. It starts at a low autism probability of ~0.4 at the lowest parts per billion of air pollution. It peaks at just under about 0.6 between 50 and 100 parts per billion of air pollution. And then … it drops again, nearing 0.4 as air pollution approaches 150 parts per billion. It is not a compelling visual argument that air pollution is linked to autism.

You can’t see the accompanying data tables behind the paywall, but they warrant a mention. The authors broke down air pollution exposure into ranges (quartiles) and then presented odds of autism in relation to each exposure range for different time points. What’s weird about the data in these tables is that the range across the first two quartiles is 9.7 to 31.8 parts per billion, yet the two quartiles differ very little and overlap quite a bit. The quartile with the lower exposure range of 9.7-16.9 often has higher odds values than the quartile with a higher range of 16.9-31.8. That, in spite of the fact that the air pollution values in the higher quartile could be three times those of the lower. Only in the quartile with exposures above 31.8 parts per billion do the odds values exceed 1, yet the figure suggests that at higher levels, probability starts to drop again.

The authors also did not control for smoking in the home or for indoor pollutants, although they did control for maternal smoking. So there’s no way to know what second-hand smoke or other indoor pollutant exposure might have been for the mothers or the children.

Finally, there’s the editorial (paywalled, sorry) that accompanied this research report, one that makes the not-so-startling observation that the increase in autism prevalence parallels an increase in autism research. I’d call that a clear example of awareness and hot science interacting with each other. The editorial author, Geraldine Dawson, I’ve already noted, often was the only other person quoted as the “outside commenter” in news stories about this study, often identified in her academic role at the University of North Carolina, Chapel Hill. In her editorial, she does not mention that the organization for which she is chief science officer, Autism Speaks, has awarded a grant to Heather Volk, lead author on this report, for almost $450,000 to do a study very similar to this one, using a different database. She also does not note that Autism Speaks has awarded a grant to a second author on this study for unrelated work. Dawson lists Autism Speaks in her affiliations at the end of the editorial but not her executive role there.

[The Volk et al. paper mentions that Autism Speaks funded travel for Volk to present these findings at a conference. Her previous study of freeways, air pollution, and autism cites funding from Autism Speaks, but in an emailed response to my queries, Volk says that funding was for a different author. The only grant I can find for a study on air pollution and autism in the Autism Speaks grant database (going back to 2006) is the one to Volk, who wrote by email that the Autism Speaks grant did not fund the current work. Perhaps the database is not complete.]

At any rate, an editorial highlighting a paper with at least two authors who have received funding from the organization for which the editorial writer is the executive science officer should have revealed as much. With that conflation, having Dawson as the sole commenter in news reports about this study isn’t exactly digging for outside commentary. Indeed, the Autism Speaks Website, in a post highlighting this research, notes that Volk is the recipient of an Autism Speaks research grant to study autism and air pollution. This association would better have been disclosed in the editorial Dawson wrote highlighting Volk’s paper. That, at least, might have pointed journalists toward real outside critique when reporting on this study.

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“what” the issue of How “Vaccination prevents Congenital Rubella Infection works with … “Support, not cure: autism is a naturally occurring human neurological variation and not a disease process to be cured.”

Rubella is an infectious disease that a vaccine can prevent. Autism not associated with an infectious disease is not. You no doubt are aware that some cases of autism are traceable to specific triggers such as this, but of course, congenital rubella carries adverse outcomes beyond autism including seizures, deafness, and other issues. Are you saying that we should not have rubella vaccination if we believe that autistic people should be treated as humans who contribute to the diversity of our species?

So far, you’re the only person asking these questions; I wasn’t aware of some public clamor for this information, which, I will add, is fairly easily available by way of a simple google search on my name.

As you probably well know (I’m assuming this is where you’re going with your weird questions), congenital rubella infection is associated with autism. It also is associated with deafness, retinal complications, profound intellectual disability, developmental delays, and multiorgan involvement. This infection during pregnancy is also associated with an increased risk of miscarriage, premature labor, and stillbirth. While autism can be co-morbid and one study suggests that the vaccine has reduced ASD incidence as a result, congenital rubella syndrome is not represented by autism. I’ve got no problem with using a vaccine to prevent this infectious disease and exposure of pregnant women at the critical developmental period (and miscarriage or stillbirth) while supporting the existence and potential of autistic people as a natural part of humanity, not as mutants or abnormals who need to be marginalized or considered a burden.